1. Field of the Invention
The present invention relates to a light-emitting device, a method for making the same, and a nitride semiconductor substrate. More specifically, the present invention relates to a light-emitting device formed from a nitride semiconductor, a method for making the same, and a nitride semiconductor substrate. In the present invention, “light-emitting device” may refer to a semiconductor element formed essentially from a nitride semiconductor substrate and a semiconductor layer laminated thereon, or may refer solely to a device sealed in resin in which a semiconductor chip is mounted on a mounting part. Furthermore, the term may refer to both of these meanings at the same time. Also, a semiconductor chip may be referred to simply as a “chip”. Also, in a chip, a substrate and an epitaxial layer formed thereon may be referred to simply as a “substrate”.
2. Description of the Background Art
White light-emitting diodes (LEDs) are currently widely used for illumination in compact electronic devices such as portable information terminals, but there is the promise that these diodes may be used in the future for illumination of large spaces or areas. In order to allow use in large spaces or large areas, the LED light output must be increased.
One method for significantly increasing light output is to efficiently output the light generated within the LED to the outside, i.e., to improve the light extraction efficiency. Examples of technologies for improving light extraction efficiency in this manner include: a light-emitting device in which a groove is formed from the surface of a nitride semiconductor layer to a substrate near a p-electrode formed on a nitride semiconductor layer laminated on the substrate (see Japanese Laid-Open Patent Publication No. 2004-87930); and a light-emitting device in which a light reflection surface is formed on a back surface of a substrate opposite from a surface on which a nitride semiconductor layer is laminated (e.g., see Japanese Laid-Open Patent Publication No. 2004-56088).
Japanese Laid-Open Patent Publication No. 2004-87930 described above gives as examples of methods for forming grooves: dry etching; wet etching; an optical method involving a laser; and mechanical methods involving dicers, scribers, or the like. Also, Japanese Laid-Open Patent Publication No. 2004-56088 above describes the forming the reflection surface on the back surface of the substrate as a groove with a V-shaped cross-section using a dicer.
These conventional technologies, however, have the following problems. If etching is used to form grooves, an adequately high etching rate cannot be used, although this depends on the material used in the nitride semiconductor substrate. In such cases, forming deep grooves within a practical etching time is difficult. Also, when etching is used to form grooves, controlling groove shape (e.g., the angle formed at the bottom of the groove between the facing side walls) is difficult.
If grooves are formed with a mechanical method such as with a dicer, the dicing surface (i.e., the side walls of the groove) acquires a layer damaged by processing or a region with damaged crystal planes. When this happens, adequate emission of light from the side wall surfaces of the groove becomes difficult due to the influence of the altered layer or the like. As a result, adequate improvement of light extraction efficiency in the light-emitting device is made difficult.
The object of the present invention is to overcome these problems and to provide a light-emitting device with improved light extraction efficiency, a method for making the same, and a nitride semiconductor substrate that can be used in making the same.